Hydraulic pump having non-radial cylinders contained in a rotor

ABSTRACT

A hydraulic pump having a rotor with pistons which slide in cylinders formed through the rotor and arranged around the axis of rotation thereof. The free ends of the pistons project from the rotor and adhere to an inclined reaction surface. On the side of the projecting pistons, the rotor is supported by a pin having a spherical head which is inserted in an axial cylindrical cavity of the rotor. The pin is supported, in turn, in a freely rotatable manner, about its own axis which is perpendicular to the inclined reaction surface. On the side away of the projecting pistons, the rotor adheres with a planar surface perpendicular to its axis of rotation, to a surface of a distributor in which the intake and delivery ports for the liquid have been formed.

United States Patent Garcea [S4] HYDRAULIC PUMP HAVING NON- RADIAL CYLINDERS CONTAINED IN A ROTOR [72] Inventor: Gillnpaolo Garcea, Milan, Italy [73] Assignee: Alia Romeo S.p.A., Milan, Italy [22] Filed: April 17, 1970 [211 App]. No.: 29,503

[30] Foreign Appficatiou Priority Data [15] 3,682,046 [451 Aug. 8, 1972 2,653,577 9/1953 Jenny ..9ll499 3,545,338 12/1970 Lucien ..91/507 FOREIGN PATENTS 0R APPLICATIONS 1,038,588 9/195 3 France ..9l/505 1,152,134 2/1958 France ..9l/506 Primary Examiner-William L. Freeh Attorney-Holman & Stern ABSTRACT A hydraulic pump having a rotor with pistons which slide in cylinders fonned through the rotor and arranged around the axis of rotation thereof. The free ends ofthe pistons project from the rotor and adhere to an inclined reaction surface. On the side of the projecting pistons, the rotor is supported by a pin having a spherical head which is inserted in an axial cylindrical cavity of the rotor. The pin is supported, in turn, in a freely rotatable manner, about its own axis which is perpendicular to the inclined reaction surface. On the side away of the projecting pistons, the rotor adheres with a planar surface perpendicular to its axis of rotation, to a surface of a distributor in which the intake and delivery ports for the liquid have been formed.

SClalmdDrawingFigures PATENIEDMH 8 I972 3.682.046

SHEET 1 [IF 2 HYDRAULIC PUMP HAVING NON-RADIAL CYLINDERS CONTAINED IN A RUIOR BACKGROUND OF THE INVENTION In the most recent years, in the field of the hydraulic applications, the need has been increasingly felt for reducing the size and thus the bulk of the devices adapted to furnish power, so as to obtain both a greater compactness of the installation and a reduction of costs. Inasmuch as these objects are achieved with high pressures and high speeds, attention has been obviously directed to pumps of the hydrostatic type which lend themselves better to the attainment of these features and which, as is known, comprise gear pumps, vane pumps, pumps having helical teeth and piston pumps. Among the latter, the ones which are most widely employed in power-transmission units and servomechanisms are gear pumps and piston pumps and, in certain case, preference is given between these latter two types, to piston pumps which can be easily built with a variable volume and are the most suitable ones for obtaining high pressures with a high efficiency and, in general, are less noisy.

Piston pumps, in turn, are divided into radial and axial pumps. From a constructional standpoint, radial pumps, though they are composed by a limited number of component parts, have severe requirements, whereas, from a functional standpoint, inasmuch as they cannot resort an automatic clearance takeup, have a shorter service life due to wear, especially whenever high performances are required with a limited bulk, as in such a case they must operate, of necessity at a high RPM rating. With these respects, axial pumps show a better perspective use since, from a constructional standpoint, they are easier to build, whereas from a functional standpoint, they afford the possibility of an automatic clearance takeup, exhibit a better resistance to the impurities of the working fluid, attain high pressures with high efficiencies and it is possible on account of their constructional features, to make high power units with, limited bulk at high RPM ratings, these factors obviously showing a tendency towards raising the specific power.

One of the factors which contributes towards reducing leakages in axial pumps is the isostaticity of the rotor, which should be free to find an equilibrium position with respect to the distributor surface. To achieve this object, several expedients have been adopted heretofore, among which, mainly, the use of universal joints or of drive-transfer shafts which are adequately flexibly connected to the rotor by means of splined joints. The methods, however, do not give any reaction, or give inadequate reactions in the direction perpendicular to the rotor axis so that it becomes necessary to support the load perpendicularly to said axis by means of a bearing mounted externally of the rotor, at the expenses, of course of the radial size.

Another approach envisaged in order to solve the problem indicated above and recently outlined in the technical literature, is that of making the rotor integral with the driving shafi, so as to provide the rotor and a shaft as a monolithic unit, and making the distributor floating by housing it on resilient supporting members or on pistons which are in communication with the high pressure chamber, but this approach is not, of course, a simple solution, or a cheaper one, either.

SUMMARY OF THE INVENTION This invention solves, in a simple and cheap way, the problen's connected with the isostaticity of the rotor of a hydraulic pump having axial pistons, by providing the rotor with a supporting member capable of counteracting the thrusts on the rotor in a direction perpendicular to the axis thereof, as originated by the pressure of the liquid and the inclination of the reaction member to whose surface the pistons adhere, with the supporting member being formed by a member having a partially spherical surface which, in turn, is freely rotatably supported about its own axis, and the latter being perpendicular to the inclined surface of the reacting member. The supporting member, in addition, is inserted into a cylindrical cavity formed in the rotor on the side away of the distributor and coaxial with the rotor.

Preferably, the rotor-supporting member is rigidly connected to the reaction member which, in turn, is supported in the pump stator by means of a bearing which is adapted to withstand both thrust and radial loads.

The invention will be described in more detail hereinafier with reference to two exemplary embodiments thereof, the description being aided by the accompanying drawing, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is an axial sectional view of an axial piston pump having a constant piston displacement and equipped with the rotor-supporting member according to the invention.

FIG. 2 is a cross-sectional view taken along the line Il-II of FIG. 1, the view looking in the direction of the arrows.

FIG. 3 is an axial sectional view similar to that of FIG. I, but showing a pump having a variable piston displacement, and

FIG. 4 is an axial sectional view taken along the line IVIV of FIG. 3, the view looking in the direction of the arrows.

DETAILED DESCRIPTION OF THE DRAWINGS The axial-piston hydraulic pump shown in FIG. 1 comprises a housing or stator 10 in the interior of which there are, substantially, a distributor 1, a rotor 2, pistons 3 and a reaction member 4 for the pistons, which has a sloping surface to which the pistons adhere. The distributor comprises a metal disc through which intake ports 7 and delivery ports 6, for the liquid to be pumped, are formed (see FIG. 2). These ports have a substantially semi-toroidal shape and are in communication, respectively, with an intake duct 11 and a delivery duct 12 formed in the stator 10. The two surfaces of the disc 1, perpendicular to the pump axis, are planar and parallel to one another. The disc I is locked within the stator and can react only with forces which are perpendicular to those surfaces.

The rotor 2 consists of a cylindrical body on whose front surface placed on the side of the distributor disc 1, are formed ports 13, through which cylindrical chambers or cylinders 14 communicate, in alternation, during the rotary motion, with the intake ports 7, and the delivery ports 6, respectively, of the disc 1. The front surface of the rotor 2 is truly planar and is perpendicular to the longitudinal axis which coincides with the axis of rotation of the rotor. Within the cylindrical chambers 14 the pistons 3 slide, and which are biased, during the intake stage, towards the sloping surface of the reaction member 4 by the agency of springs 5.

In the example shown, the longitudinal axis of the cylindrical chambers 14 are a part of a theoretical cylindrical surface, but they could belong also to a conical surface whose apex is on the side of the disc 1 and lies on the axis of rotation of the rotor.

The rotor 2 is driven to rotation in the direction of the arrow 15 (see FIG. 2) by a drive shaft 16 supported in the stator 10 by the agency of a ball bearing 17 and is connected to the cylindrical body of the rotor 2 by an arbor 18 which carries, in the neighborhood of both its ends, crenellations l9 and 20, respectively, which are in mesh with the end of the drive shaft 16 and the rotor 2. The arbor 18 can freely go through limited axial displacements and also the transfer of the rotary drive through the crenellations takes place with a certain clearance so as to allow for a certain freedom of motion of the rotor.

The reaction member 4 situated on the side away from a distributor disc 1 consists of a metal body having the reaction surface for the pistons which is truly planar and smooth.

In the example shown in FIG. 1, since a pump having a constant piston displacement is the question, the inclination of the reaction member 4 is fixed. The pistons 3, forced to adhere to the surface of member 4 and due to their motion concurrent with the rotor 2 about the axis thereof, carry out a reciprocal motion in the direction of their axis, so as to cause the pump to be operative. The pistons 3 can have a spherical head, as shown in FIG. 1, or they can rest against the inclined surface of the member 4 by means of pads.

Under steady conditions, the rotor 2 undergoes, in addition to the inertial forces due to the reciprocations of the pistons 3, the driving moment and a number of reactional forces: (a) the reaction of the distributor disc 1, which is perpendicular to the disc and passes through the center of gravity of the semitoroidal delivery port 6; (b) the resultant of the reactions of the inclined surface of the member 4 on the individual pistons 3 due to the pressure: this is perpendicular to said surface and passes through the center of gravity of the portion of the elliptical line described by the centers of the spherical heads of the pistons 3 on an ideal plane parallel to the inclined surface of the member 4.

To balance the rotor 2, it is necessary that an external constraining member may afford a reaction on a plane perpendicular to the axis of rotation of the rotor.

According to the present invention, this constraining member is a support for the rotor 2 on the side of the reaction member 4. The supporting member, in the example shown, is a pin 27 which is rigidly connected to the member 4 by a screw and nut locking arrangement 21. The pin 27 could also be made integral with the member 4. The pin 27 has a spherical head 22 which is inserted into a cylindrical chamber 23 formed in the rotor 2 and coaxial therewith.

The axis of the pin 27 is perpendicular to the sloping surface of the member 4 and since the latter is supported in a lid or cover 26 of the stator 10 of the pump by a ball bearing 8, the pin 27 with the member 4 can freely rotate about its own axis. By so doing, the frictional forces are reduced to nil since, with the exception of a negligible spinning motion, both the relative motion between the spherical head 22 of the pin 27 and the cylindrical cavity 23 of the rotor 2, and the relative motion between the pistons 3 and the sloping surface of member 4 are nullified.

As clearly shown in the foregoing, the supporting member provided according to the invention, afiords, at a minimum cost and in an extremely simple manner, the solution of the problems connected with the isostaticity of the rotor 2, with the weight and the radial bulk of the pump being reduced while increasing the efficiency.

Another special feature of the present pump lies in that the load applied to the bearing 8 is a resultant force which, passing in the interior of the pitch circle travelled over by the centers of the balls of the bearing, does not originate any upsetting action which would prevent the use of a mere thrust bearing and would render objectionable the operation of a radial and thrust bearing having a deep groove. Since the external forces acting on the assembly formed by the rotor 2 and its pistons and springs and the reaction member 4 with its pin 27 are reduced to the resultant of the hydraulic pressures which act on the rotor in correspondence with the plane of the distributor disc 1, and the resultant force in question is just the load which is active upon the bearing 8. Such a resultant is, obviously, perpendicular to the plane of the distributor disc 1 and passes through the center of gravity of the areas which are under pressure: according to the invention, the diameter of the bearing 8 has such a size that the resultant force aforesaid, which can be geometrically measured on the drawing, passes inside the pitch circle which is travelled over by the centers of the balls of the bearing.

It has been said that in the example shown in H0. 1, for a pump having a constant piston displacement, the reaction member 4 has a fixed slope. In pumps having a variable piston displacement, the member 4 should be capable of varying its slope continuously, from zero to a maximum magnitude, and vice versa.

This case is illustrated in FIGS. 3 and 4, wherein the parts of the pump which correspond to those of the pump of FIG. I are indicated by the same reference numerals. The reaction member 4 and the supporting pin '27 can rotate in the bearing 8, which, in this case, is

fastened to a stirrup 28 having two ears 29 and 30 parallel and diametrically opposite to one another and lying on planes perpendicular to the supporting surface of the pumping pistons 3. By the cars 29 and 30, the stirrup 28 is hinged to two coaxial pins 31 and 32 integral with the stator 10. The axis of the pins 31 and 32 intersects the axis of rotation of the rotor 2 and is perpendicular thereto. An actuating plunger 33 (FIG. 3) can be shifted in a cylindrical chamber 34 formed in the stator 10 and is connected by a crank 35 to the stirrup 28. By varying the pressure differential in the two spaces of the cylindrical chamber 34, it is possible to vary also the inclination of the stirrup 28 and of the reaction member 4 and thus the volume of the pump. If the rotor is supported, according to the conventional art, by an external radial bearing, the suspension ears of the stirrup must be, of necessity, at least substantially tangent to the outside diameter of the bearing, but if, to

support the rotor, the arrangement according to this invention is adopted, the ears 29 and 30, whose axis intersects now the axis of rotation at the point where the center of the spherical head 22 of the pin 27 lies (see FIG. 4), can virtually be tangent to the outer cylindrical surface of the rotor 2, with the radial bulk of the pump and the bulk and weight of the stirrup being significantly reduced.

The invention has been described by way of nonlimiting example with reference to the embodiments shown in the drawings, it being understood that anyone skilled in the art may introduce a number of constructional modifications and changes without departing from the scope of this invention.

What is claimed is:

l A hydraulic pump of the type having a rotor provided with pistons sliding in cylinders arranged around the axis of rotation of the rotor, said cylinders having their axes not perpendicular to said axis of rotation, each piston having a projecting portion protruding from one side of the rotor, said projecting portion adhering to a reaction surface which is inclined with respect to the axis of rotation of the rotor, whereby the pistons are caused to reciprocally slide inside their cylinders when the rotor is rotated, said reaction surface being provided by a thrust plate freely rotatable around an axis which is perpendicular to the reaction surface and passing through the center of an ellipse which is defined onto the reaction surface by the interception points of the axes of the cylinders with the reaction surface, on the opposite side of the rotor, a front surface adhering to a corresponding stator surface through which intake and delivery ports are formed, said thrust plate being in contact with the rotor through two contact components, one of said contact components being directly provided on the rotor so as to rotate around the rotation axis of the rotor, and the other contact component being directly provided on the thrust plate so as to rotate around the rotation axis of the reaction surface, one of said contact components being partially spherical and said thrust plate being rotated by the rotor around said rotation axis perpendicular to the reaction surface.

2 A hydraulic pump of the type having a rotor provided with pistons sliding in cylinders arranged around the axis of rotation of the rotor, said cylinders having their axes not perpendicular to said axis of rotation, each piston having a projecting portion protruding from one side of the rotor, said projecting portion adhering to a reaction surface which is inclined with respect to the axis of rotation of the rotor, whereby the pistons are caused to reciprocally slide inside their cylinders when the rotor is rotated, said reaction surface being provided by a thrust plate freely rotatable around an axis which is perpendicular to the reaction surface and passing through the center of an ellipse which is defined onto the reaction surface by the interception points of the axes of the cylinders with the reaction surface, on the opposite side of the rotor, a front surface adhereing to a corresponding stator surface through which intake and delivery ports are formed, said thrust plate being in contact with the rotor through two contact surfaces, one of said contact surfaces being provided for the rotor so as to rotate aa t'argssarmsas'aas rta sat, rotate around the rotation axis of the reaction surface, one of said contact surfaces being cylindrical and the other contact surface being partially spherical and said thrust plate being rotated by the rotor around said rotation axis perpendicular to the reaction surface, the contact which is partially spherical being rigidly connected to the reaction member, and a bearing of the type provided for both radial and thrust loads supporting said reaction surface. 7

3 The hydraulic pump according to claim 2, including a stator for the pump, and the bearing being fastened to the pump stator.

4 The hydraulic pump according to claim 2, including a stator for the pump, a stirrup supported in the pump stator by two diametrically opposite hinges, the pivoting axis of the hinges passing through the center of the surface which is partially spherical.

S The hydraulic pump according to claim 2, characterized in that the bearing is a ball-bearing and is of such a size that the resultant of the hydraulic pressures acting on the rotor at the plane of the intake and delivery ports, passes within the pattern followed by the centers of the balls of said bearing. 

